1. Field of the Invention
The present invention relates to a nitride semiconductor light emitting device, more particularly, which is highly resistant to Electrostatic Discharge (ESD).
2. Description of the Related Art
Recently, a group III-V nitride semiconductor (hereinafter “nitride semiconductor”) has been broadly used as a light emitting diode (LED) for emitting blue or green wavelength light or a semiconductor material for a laser diode (LD). The nitride semiconductor also has found applications as a light source of various products such as natural color display boards, traffic lights, image scanners and lighting devices. Here the nitride semiconductor device denotes a GaN-based semiconductor material having a composition expressed by InxAlyGa1-x-yN, where 0≦x≦1, 0≦y≦1 and 0≦x+y≦1. In utilizing this nitride semiconductor device, greater significance has been imparted not only to light emitting capability but also reliability thereof. The nitride semiconductor light emitting device is typically susceptible to Electrostatic Discharge (ESD), especially reverse ESD. Thus ESD withstand voltage of the light emitting device is a determinant factor of reliability.
Various studies have been conducted to suppress ESD-induced damage to the nitride semiconductor light emitting device. For example, in a conventional method, a GaN-based LED is connected in parallel to a Si-based zener diode to prevent the light emitting device from ESD. However, such a method requires a separate zener diode to be bonded and assembled, thereby considerably increasing material and process costs and hampering miniaturization thereof. In another conventional method, U.S. Pat. No. 6,593,597 discloses a technology of integrating an LED device and a Schottky diode on the same substrate and connecting them in parallel with each other to protect the light emitting device from ESD.
FIG. 1 is a cross-sectional view illustrating a conventional nitride semiconductor light emitting device having a Schottky diode installed therein. Referring to FIG. 1, the light emitting device (LED) includes buffer layers 12a and 12b, a first n-type nitride semiconductor layer 14a, an active layer 18, a p-type nitride semiconductor layer 22, a transparent electrode 24 and an n-electrode 26 formed sequentially on a sapphire substrate 11. Also, the Schottky diode is formed separate from the LED structure on the sapphire substrate 11. The Schottky diode includes a second n-type nitride semiconductor layer 14b, a Schottky contact electrode 28 and an ohmic contact electrode 30.
The transparent electrode of the LED structure is connected to the ohmic contact electrode 30 and the n-electrode 26 of the LED structure is connected to the Schottky contact electrode 28. Accordingly, the LED structure is connected in parallel to the Schottky diode. In the light emitting device structured above, reverse ESD applied may be discharged through the Schottky diode. Therefore, with the reverse ESD voltage applied, most current flows through the Schottky diode in place of the LED diode, shielding the LED structure from ESD.
Yet, this method for shielding ESD via the Schottky diode cumbersomely requires a separate Schottky contact to be made, increasing manufacturing costs of the device. That is, the LED device area should be separated from the Schottky diode area. Moreover, an electrode material for forming the Schottky contact and an electrode material for forming an ohimic contact should be deposited separately on the second n-type nitride semiconductor 14b made of an n-type GaN-based material.